Telephone installations already exist in which ordinary extensions are connected by inside lines to a private automatic exchange which is itself connected to the telephone network, i.e. a private automatic branch exchange or PABX. Additional intercommunication means connected between the private exchange and privileged extensions provide said privileged extensions with advanced telephone functions such as the filtering of telephone calls made to a first extension so that they are diverted to another.
The term "filtering" is used herein to designate the operation whereby calls intended for a given extension are systematically intercepted and sent to another extension in order to enable said calls to be filtered or "vetted", e.g. by a secretary. The term "ordinary" extension is used herein to designate a standard telephone set suitable for direct connection to an outside telephone line, e.g. a French type S63 set or an American 500 series set. Filtering is said to be "supervised" when all of the information relating to said interception function (identity of the filtering extension, busy states of the other extensions) is available at the filtering extension prior to any filtering action.
In the past, the additional intercommunication means have constituted an additional private telephone exchange interposed between the PABX and the privileged extensions. These privileged extensions include private call keys each associated with an inside party in order to enable calls to be made to said parties, together with function keys, in particular for the purposes of intercepting calls, holding calls, and transferring them. Each extension has several outside lines available via the PABX for the purpose of making outside calls. Display means may be provided to indicate the busy state of extensions and also the busy state of outside lines.
Such an installation serves to interconnect all of the people in a given service or in a given geographically-determined department with one another and with the outside (naturally within the limit imposed by the number of private call keys available). Such an installation can also be used for filtering telephone calls intended for a given extension to a different extension within a boss-secretary pair such that a first extension (secretary) intercepts calls to any of the parties in an installation and subsequently puts calls through to at least one other extension (boss).
This type of installation suffers from the drawback of being expensive, particularly when there are relatively few privileged extensions since the cost of the central system and the unit cost of said extensions each accompanied by its inside line become very high.
Further, cabling the inside lines which interconnect the PABX to the additional intercommunication means and also the inside lines which interconnect the additional intercommunication means and the extensions is expensive since the inside lines are constituted by several telephone pairs (usually three) and laying the cables in the first place is often difficult and subsequent removals are rarely easy to perform.
There also exist telephone installations in which the extensions are interconnected by additional connections conveying computer signals. A computer signal receiver housed in each extension serves to interchange signalling via said additional computer connections concerning, in particular, the filter states and the busy states of the various extensions. The drawbacks of such an installation include the same problem of cabling the additional connections, the high cost of each extension, and finally the unergonomic software controlling the interchange of computer signals.
The object of the invention is to remedy these drawbacks. To this end. the invention provides a telephone installation enabling the telephone facilities of the installation to be augmented by a radio link which conveys signalling, in particular for the purpose of filtering telephone calls intended for one extension to other extensions while supervising said filtering. This installation is particularly simple and reliable and makes it possible to increase the capabilities of the extensions without requiring additional inside lines to be cabled between said extensions.